Method of manufacturing vacuum tube devices



March 24, 1942. R. SCHARFNAGEL METHODS OF MANUFACTURING VACUUM TUBE DEVICES Filed April 14, 1939 INVENTOR. RUDOLFJ'C'l/ARFAMGEL ATTORN FIG.3.

9 90098 G 9 8 0 0 S GQGQOQ Patented Mar. 24, 1942 METHOD OF MANUFACTURING VACUUM TUBE DEVICES Rudolf Scharfnagel, Stuttgart, Germany, assignor to C. Lorenz Aktiengesellschaft, Berlin- Tempelhof, Germany, a company Application April 14, 1939, Serial No. 267,743 In Germany April 14, 1938 2 Claims.

This invention relates to methods of manufacturing vacuum tube devices, particularly electron discharge devices having a vessel wholly or partially made of metals or metallic alloys.

It is a well known expedient in connection with vacuum tube devices, such as electron discharge tubes and the like, to employ entirely or partially metallic materials for making the vessel in order to secure the desired stability and rigidity against mechanical stresses and to facilitate the heat conduction to the surrounding medium during operation. The manufacturing of electron discharge tubes of this type is somewhat disadvantageous due to the fact that the lead-in conductors to the various electrodes must be carried through the metallic wall or walls and be insulated therefrom, and that it is rather difficult to provide perfect vacuum seals between these metallic members. It has therefore been proposed in the past to first fix the electrodes in a supporting member of a ceramic substance and to subsequently attach said ceramic support to the metallic envelope of the tube.

My invention has for its object to provide new and useful improvements in methods of producing electron discharge tubes of the last mentioned design. This is realized according to the main feature of the invention by first fusing together an electrode supporting member of a ceramic substance and a disc of glass of larger diameter, then placing the lead-in conductors in their proper positions in said glass-covered supporting member and finally intimately uniting the outer portion of said glass disc with the metallic envelope of the tube to a perfect vacuum seal. This seal is preferably made in such manner that the edge or flange of the metallic envelope is heated by high frequency currents to a temperature at which the glass is converted from its solid to its soft condition so as to form a vacuum-tight con nection with the flange of the envelope.

The invention will be more readily understood from the following description taken in conjunction with the accompanying drawing, in which- Fig. 1 is a cross sectional view through an arrangement suitable for use in connection with the first steps of my method of manufacturing discharge tubes, Fig. 2 is a cross-sectional detailed view of an electrode lead-in conductor with a glass collar for use in the further step of the process, while Fig. 3 shows a cross sectional view of the device for effecting the final step in the manufacturing of discharge tubes according to the invention.

Referring to Fig. 1 which shows means for accomplishing the first and further steps according to my method, a indicates a supporting member of any suitable ceramic material. This supporting member which is provided with a number of holes arranged circularly thereon at a diameter indicated by letter 1) in this figure is placed in the interior of a metallic die 0. A disc or plate I) of glass of a diameter which substantially corresponds to the outer diameter of the die 0 covers the upper surface of the supporting member a. A heating device d, such as a coil, for instance, arranged around the outer boundary of the die a is adapted to subject the die together with the supporting member a and the glass disc b to a first heat treatment. This heating device d is placed in the open part of a cup-shaped heat insulating body e which e. g. may consist of diatomaceous earth.

The first heat treatment of the members a, b and 0 above referred to is continued until the temperature is reached at which the glass disc I) is converted from its solid to its viscid condition, whereupon an acicular flame f is directed from below exactly onto the center of the supporting member a. The additional heat thus applied to the center of the glass through the ceramic substance causes the glass to soften and to adhere or stick on the upper surface of the supporting member a. On account of the concentrated heat applied to the center portion of the glass, the softening proceeds concentrically outwards. When the softening of the glass has exceeded the above mentioned diameter v, the lead-in conductors are fixed in their positions. For this purpose each conductor has beforehand been equipped with a collar of glass as shown in Fig. 2, in which E denotes a conductor and B a glass collar. The lower end of the conductor E is now inserted into its appropriate hole through the top-layer of soft glass. This procedure must be carried out relatively slowly in order to allow the soft glass thus cooled by the inserted metallic conductor to again assume its proper temperature under the influence of the flame f, whereupon the lead-in conductors are gradually pushed down one after the other until the lower surface of the collar B touches the soft glass layer b. These two glass members soon merge into each other and form a perfect seal.

It is important in carrying out these steps that the member 0 is made of metal and that there is provided an intermediate annular plate h of asbestos between the outer edge of the glass disc 12 and the supporting upper end of the die 0. The mass of this member must be so chosen that it becomes heated more slowly than the members a and b which are to be intimately united with one another so as to maintain the outer flange of the glass disc b at a relatively low temperature with respect to that of its central portion. The cylindric wall of the die 0 is provided with radial apertures i in order to secure air supply to the flame f. It is possible in accordance with the above disclosed method to provide a perfect vacuum seal between the glass disc I) and the ceramic sup porting member a, and also to fix the lead-in conductors in the supporting member in a simple and adequate manner. The finished product is then removed from the die and permitted to cool.

The glass-coated supporting member a carrying the required number of lead-in conductors may now be used as a closure member for a metallic vacuum tube vessel which may form the anode of a triode, for example. Such metallic vacuum vessel and the closure member may then be sealed together in a further operation hereinafter more closely described in conjunction with the Fig. 3.

A metallic tube K having a conical portion and a flange at its open end substantially flat at right angles to the major axis of the tube is first inserted in a supporting tubular member L of ceramic material having a conical upper inner surface so that the tube or envelope K abuts against the porous conical surface of the ceramic member L. The shape of the cones is so chosen as to provide a reliable seat therebetween which is not endangered in any manner by compressed air as introduced through appropriate means M being used for cooling purposes during the further procedure. The glass-coated supporting member (1 together with an electrode system meanwhile connected to the lead-in conductors fixed in said member is now brought in proper position so that the electrode system projects into the interior of the envelope, while the outer portion of the glass disc b extending beyond the ceramic supporting member a rests on the flat flange of the envelope K. This assembly is now placed in a pre-heating device d for the purpose of being pre-heated as heretofore described. When the temperature is reached at which the glass changes from its solid to its soft state, which approximately corresponds to the moment when the metal turns blue, the pre-heating device is removed and replaced by a high frequency heater coil. When this coil is effectively connected to a high frequency source, the upper flange of the metallic envelope assumes such a high temperature that the glass thereon is converted into its fluid state. The upper flange of the envelope K is preferably provided with an outer circumferential extension P in order to definitely limit the glass flow to the desired size. After the elapse of few seconds, this sealing procedure is finished. The product thus obtained is a metallic vacuum tube envelope with which the lead-in conductors form a perfect vacuum seal.

The ceramic supporting member a preferably consists of a very porous material which in addition to the holes adapted to receive the lead-in conductors may be provided with a number of bores or cavities so as to permit the fluid glass to flow into these cavities. The metallic envelope may preferably be used as the outer anode of a discharge device. The evacuation pipe may be formed at the end of the envelope remote from that in which the lead-in conductors are sealed.

What is claimed is:

1. The method of manufacturing vacuum tube devices comprising the steps of placing a ceramic closure member provided with holes in the interior of a metallic die forming part of a heater device, covering said closure member and the upper end of said die with a glass disc of adequate size, pre-heating the closure member and disc located in said heater device to a temperature at which the glass is converted from its solid to its soft state to fuse said glass disc onto said closure member, applying additional heat by a flame to the center of said closure member to partially convert the glass from a soft to a fluid condition, pushing glass collar equipped lead-in conductors through the fluid layer of glass and said holes in the said closure member, cooling the heater device, connecting an electrode system to said leadin conductors, inserting the glass-covered closure member with its electrode system into a metallic envelope having a substantially flat sealing surface at right angles to its major axis, adjusting the projecting portion of said glass disc in abutting relation with the flat surface of said envelope, pre-heating said abutting surfaces in a heater device, and sealing said surfaces together in a high frequency current heat treatment.

2. The method as set forth in claim 1, which consists in the further step of cooling the metallic envelope with compressed air during the heat treatment.

RUDOLF SCHARFNAGEL. 

